Publisher Summary This chapter discusses fourier transform infrared microscopy. Fourier Transform Infrared Spectroscopy (FTIR) coupled with microscopy provides unique opportunities to study change, based on the complexity and specificity of the infrared spectrum and the dimensional resolution of the microscope. The results described, clearly demonstrate the capabilities of FTIR micro spectroscopy mapping techniques to investigate weathering associated degradation processes in PVC formulations. Employing these techniques, depth profiles, from the exposed surface, can be obtained for many of the degradation species. Formation of the acid chloride and beta chlorocarboxylic acid differs depending on exposure type and presence of pigment. Under accelerated conditions the conversion of the acid chloride to the chlorocarboxylic acid appears to occur very fast for all formulations. In the outdoor exposed samples this effect is present for the unpigmented formulations. The presence of TiO2 decreases the rate of conversion. Additionally, the level of oxidation species, near the exposed surface, is higher for the outdoor exposed samples. This may have implications in the deterioration of the mechanical properties associated with weathering. Finally, it is difficult to draw conclusions regarding a direct correspondence between the accelerated and outdoor results in terms of extrapolating performance expectations.